AppEngine: Query datastore for records with value

Question

I created a new property for my db model in the Google App Engine Datastore.

Old:

class Logo(db.Model):
  name = db.StringProperty()
  image = db.Blo         


        

Answer 1

According to the App Engine documentation on Queries and Indexes, there is a distinction between entities that have no value for a property, and those that have a null value for it; and "Entities Without a Filtered Property Are Never Returned by a Query." So it is not possible to write a query for these old records.

A useful article is Updating Your Model's Schema, which says that the only currently-supported way to find entities missing some property is to examine all of them. The article has example code showing how to cycle through a large set of entities and update them.